1. Field of the Invention
The present invention relates to an ophthalmic apparatus which performs examination or measurement of an examinee's eye.
2. Description of Related Art
There is known an ophthalmic apparatus such as a refractometer, a tonometer and a fundus camera, which performs examination or measurement of an examinee's eye, and the ophthalmic apparatus detects an alignment condition of the apparatus with respect to the eye by picking up an image of an alignment target in a spot shape, a ring shape or other shapes which is projected onto an anterior segment (a cornea) of the eye along with an image of the anterior segment by using a two-dimensional image-pickup element, and based on a result of the detection, automatically performs alignment of the apparatus with respect to the eye.
In such an apparatus, light of the alignment target often doubles as light for illuminating the anterior segment. For this reason, projection light intensity of the light of the alignment target and/or gain of the two-dimensional image-pickup element which picks up the alignment target image with the anterior-segment image are set to be higher in order to display the anterior-segment image brightly or to pick up the alignment target image clearly. However, if the projection light intensity of the light of the alignment target and/or the gain of the two-dimensional image-pickup element are set to be higher, there is a possibility that the alignment target image cannot be detected because of scattered light (noise light) from the anterior segment, depending on characteristics of the eye or an environment where the apparatus is placed. For example, if the eye has microcoria, the light of the alignment target (especially, the alignment target in the ring shape) is reflected and scattered by an iris of the eye and the scattered light enters the image-pickup element, which may have a detrimental effect on the detection of the alignment target image. In addition, if light intensity of extraneous light such as light of a light (illumination) in a room where the apparatus is placed is high, the extraneous light is reflected and scattered by the anterior segment and the scattered light enters the image-pickup element, which may have a detrimental effect on the detection of the alignment target image.